Time relays, counters or relays frequently meet the requirements for a universal control device only to a limited extent, particularly in the field of automation technology for the automation of complex logical linkages, error processes or timing. Complex SPS (stored program control) systems are often over-dimensioned with regard to their technical equipment features and are consequently too expensive in production.
In order to close this gap, compact control modules are known which offer the user the advantage that he can realize a great number of applications from the lower performance range with only one automation component. Depending on the model and the expansion, between 4 and 48 inputs or outputs, referred to below as I/O, can be handled with compact control modules of this type available in the market. A signal arriving from a bus terminal subscriber such as a sensor via an input is processed by the control module and/or conducted to a data bus, and a signal arriving from the data bus or a processed signal arriving via an input is conducted via an output to a bus terminal subscriber, such as an actuator.
Such a compact I/O control module thus generally links signals arriving via input modules according to a defined control logic and then outputs signals via the output modules.
The number and types of I/O channels of today's compact I/O modules are fixed, however, and comprise, for example, 2 inputs and 2 outputs, wherein, for instance, 1 input is provided for digital signals and 1 input for analog signals.
The linking of the input signals and the generation of the output signals by the compact control module is thus performed for the fixed number of I/O channels. Fixed physical interfaces for connection can be assigned to the I/O channels, so that the input/output modules are plugged into corresponding sockets, for example. Alternatively, logical interfaces can also be assigned to the I/O channels at the control module, so that the linkage of each input/output channel to the control module takes place via a common physical interface, using a data bus.
A substantial disadvantage of prior art is fundamentally that there are always only a fixed number of inputs and outputs for such control modules. Every expansion of I/O channels is cost-intensive and can only be done as a rule with additional use of the data bus or an additional data bus.
If a data bus is used, it is at least necessary also to address the input/output modules.